Simplify the expression. $(3z^{3}-3z^{2}+6z)(-5z^{4}+2z)$
Solution: First use the distributive property. $ 3 z^3 (-5 z^4) + 3 z^3 (2 z) - 3 z^2 (-5 z^4) - 3 z^2 (2 z) + 6 z (-5 z^4) + 6 z (2 z) $ Simplify. $-15z^{7}+15z^{6}-30z^{5}+6z^{4}-6z^{3}+12z^{2}$